Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) some other standards. Non-CDMA systems include the AMPS and GSM systems.
Wireless communication systems typically include a plurality of base stations. In CDMA systems, the base stations are differentiated by their scrambling code. In addition, base stations within a system may communicate on one or more frequencies. Neighboring systems often utilize different frequencies as well. Periodically, a mobile station needs to acquire a system, such as upon power-up or when traveling near the edge of an already acquired system. System acquisition begins with locating one or more frequencies used by a system. Subsequently, the scrambling code and its phase must be identified in order to communicate with any particular base station. Systems based on IS-95 and its progeny use a common scrambling code. The base stations are differentiated by a unique offset in the common scrambling code. Systems such as W-CDMA differentiate base stations with unique scrambling codes. Various searching techniques are known in the art for acquiring base stations at a given frequency. Acquisition time is a function of the time required to locate the frequency of a system as well as the time required to search and acquire the scrambling code of a base station on that system.
It is desirable for a mobile station to acquire base stations as rapidly as possible. Upon initial acquisition, users appreciate quick response time, so the acquisition time should be minimized. Furthermore, prompt acquisition of neighbor base stations allows the mobile station to communicate with the optimal set of base stations available. A mobile station communicating with the best set of base stations minimizes required transmit power for a given communication performance level, which results in system resources being allocated efficiently. This results in maximization of system capacity, as well as power reduction in the mobile station. Reduced power in the mobile station translates to extended communication and standby times for a given battery configuration, or reduced battery requirements (size, weight and cost), or both. Minimizing system acquisition time facilitates realizing these benefits. Minimizing the time required to scan potential system frequencies can reduce system acquisition time. There is therefore a need in the art for reducing the time required for frequency scan in acquisition.